1. Field of the Invention
The present invention relates to a stack structure formed by stacking a plurality of including at least one substrate substrates and a method of manufacturing the same.
2. Description of the Related Art
In recent years, small reactors called “microreactors” have been developed and put into practical use. Microreactors are small reactors which cause a plurality of kinds of reactants such as raw materials, reagents, and fuels to react with each other while mixing them. The microreactors are used for chemical reaction experiments in the microdomain, drug developments, artificial organ developments, genome/DNA analysis tools, and fundamental analysis tools for micro-fluid engineering. A chemical reaction using a microreactor has characteristic features different from those of a normal chemical reaction using a beaker or flask. For example, since the entire reactor is small, the heat exchange effectiveness is very high, and temperature control can efficiently be executed. For this reason, even a reaction which needs fine temperature control or a reaction which requires abrupt heating or cooling can easily be done.
More specifically, a microreactor has one or more channels (flow paths) which make reactants to flow and a reactor (reaction tank) in which the reactants react with each other. In Jpn. Pat. Appln. KOKAI Publication No. 2001-228159, a silicon substrate in which a trench is formed in a predetermined pattern and a PYREX (registered trademark) substrate made of glass are stacked and anodic-bonded, thereby forming a channel in the closed region between the two substrates. The term “anodic bonding” indicates a bonding technique. In this technique, a positive electrode is arranged on the silicon substrate while a negative electrode is arranged on the glass substrate in a hot environment. A high voltage is applied between both electrodes to generate an electric field in the glass substrate. Oxygen atoms in the glass substrate, which have negative charges, are moved to the silicon substrate side so that the oxygen atoms in the glass substrate are interatomic-bond to silicon atoms in the silicon substrate at the interface between the glass substrate and the silicon substrate. This technique is known as excellent especially in substrate bonding because substrates can be bonded without using any adhesive, or substrates can be bonded in air.
An attempt has been made to alternately stack a plurality of glass substrates and a plurality of silicon substrates and anodic-bond them to create a microreactor having a stack structure. In this case, it is difficult to bond silicon substrates to both surfaces of a glass substrate. Hence, a stack structure can hardly be manufactured. As shown in FIG. 12A, in the first anodic bonding step, a silicon substrate 301 and glass substrate 302 are arranged while making one surface 302a of the glass substrate 302 contact one surface 301a of the silicon substrate 301. A voltage is applied between them to generate an electric field in the direction of solid arrows and cause bonding at the interface between the surfaces 301a and 302a. Subsequently, in the second anodic bonding step, as shown in FIG. 12B, a new silicon substrate 303 and the glass substrate 302 are arranged while making one surface 303a of the silicon substrate 303 contact the other surface 302b of the glass substrate 302. A voltage is applied between the silicon substrates to generate an electric field in the direction of solid arrows. The direction of this electric field is reverse to the direction (broken arrows in FIG. 12B) of the electric field in the first anodic bonding step. This adversely affects the bonding between the silicon substrate 303 and the other surface of the glass substrate 302 which is anodic-bonded to the silicon substrate 301 in the first anodic bonding step.